Installing a grease trap is not a DIY project. It involves licensed plumbing work, municipal permits, an inspection before the unit goes into service, and, in most cities, approval from the local pretreatment or FOG control program. If you are opening a new restaurant or retrofitting an existing kitchen, understanding the installation process helps you budget correctly, ask the right questions, and avoid costly mistakes. Need to find a licensed grease trap installation contractor in your area? Search at greasetraplocator.com.
Why the Installation Process Matters
A grease trap that is installed in the wrong location, undersized for your kitchen's flow, or plumbed incorrectly can fail your municipal FOG inspection, generate fines, and require expensive rework. Some municipalities will not issue a Certificate of Occupancy for a food service establishment until the grease trap passes inspection. Getting the process right the first time saves time, money, and headaches during the busiest stretch of a restaurant opening.
Step 1: Determine What Type of Unit You Need
Before pulling a permit, you need to know which type of grease trap or interceptor your jurisdiction requires.
Hydromechanical grease interceptors (HGI): compact units that mount under the sink or in a floor vault. Rated in gallons per minute (GPM) of flow, typically 20 to 50 GPM. Most common in small to medium restaurants and food trucks with indoor installation. Governed by ASME A112.14.3 standard.
Gravity grease interceptors (GGI): large concrete, fiberglass, or polyethylene tanks installed outside or in the ground. Rated in gallons of capacity, typically 500 to 2,000 gallons. Required by many municipalities for high-volume operations. Governed by PDI G-101 and local pretreatment specifications.
Automatic grease removal devices (AGRD): motorized units that automatically skim and remove FOG on a timed cycle. Used in tight spaces where a large interceptor is not feasible.
Your local FOG control office or plumbing department will tell you which standard applies in your jurisdiction and what minimum size you need. Do not skip this step, arriving with the wrong unit wastes money and delays your opening.
Step 2: Size the Unit Correctly
Sizing is based on the fixtures that will drain into the trap: the number of sinks, dishwashers, floor drains, and cooking equipment. Two common sizing methods are used:
Flow rate method (HGI): Calculate the total flow rate of all connected fixtures in gallons per minute. The trap must be sized to handle that total flow.
Grease retention capacity method (GGI): Based on the total volume of FOG the kitchen produces during peak service, the pump-out frequency, and the hydraulic detention time required by the local standard.
A licensed plumber who has worked with your municipality's FOG program will run these calculations for you. Oversizing wastes money; undersizing causes compliance failures.
See our grease trap sizing guide for detailed sizing formulas and examples.
Step 3: Apply for a Permit
Almost every jurisdiction requires a permit for commercial grease trap installation. The permit application typically requires:
- A plot plan or kitchen layout showing where the trap will be located
- Plumbing drawings showing all fixtures that will connect to the trap and the drain line routing
- The unit's make, model, and certification documentation (PDI or ASME certification)
- The name of the licensed plumbing contractor performing the work
Some municipalities also require pre-approval from the local wastewater utility or sewer authority before issuing the plumbing permit. In Los Angeles, for example, the Bureau of Sanitation reviews the installation plan before the building department issues the permit.
Permit fees range from roughly $50 in smaller jurisdictions to several hundred dollars in major cities. Processing time varies from a few days to several weeks depending on the city. Factor this into your opening timeline, inspectors cannot approve a grease trap installation that was done without a permit.
Step 4: Hire a Licensed Plumbing Contractor
Grease trap installation must be performed by a licensed plumber in every state. In many jurisdictions, the contractor must also hold a separate specialty license or certification for grease trap work.
When interviewing contractors:
- Ask for their plumbing license number and verify it with your state licensing board
- Ask whether they have installed units in your specific jurisdiction before, local experience matters because inspectors in different cities have different requirements
- Ask whether they will pull the permit on your behalf (most experienced contractors handle this)
- Ask for references from recent commercial kitchen installations
Get at least two quotes. Large commercial jobs, outdoor gravity interceptors with significant excavation, can run $10,000 to $30,000 or more. Smaller indoor HGI installations under a sink typically run $800 to $2,500 including labor and materials.
Step 5: The Installation Process Itself
Indoor hydromechanical interceptor:
- Shut off water to the affected sink fixtures
- Remove existing P-trap and drain connections
- Mount the interceptor (under-sink models bolt to the cabinet floor; some hang from the wall)
- Connect inlet from sink drain; connect outlet to the building drain line
- Install clean-out access ports if not already on the unit
- Fill and test for leaks
- Verify flow in accordance with manufacturer GPM specification
Outdoor gravity interceptor:
- Excavate to required depth (typically 6 to 10 feet, depending on inlet/outlet elevations)
- Set the tank (concrete requires a crane; fiberglass tanks can sometimes be lowered by hand with equipment)
- Connect inlet pipe from building; connect outlet pipe to sewer lateral
- Backfill and compact around the tank
- Install access risers to bring manhole covers to grade
- Connect all kitchen drain lines to the building sewer line running to the interceptor inlet
- Pressure test the drain connections
Duration: indoor HGI installations typically take 2 to 4 hours. Outdoor GGI installations with excavation typically take 1 to 3 days depending on soil conditions, tank size, and crew size.
Step 6: Schedule the Inspection
Before the grease trap can go into service, the installation must be inspected by both the building/plumbing department and, in many cities, by the wastewater utility. The plumbing inspection confirms the work was done per the approved drawings and applicable code. The FOG or pretreatment inspection confirms sizing, placement, and access are compliant.
Common reasons inspections fail:
- The trap is smaller than the approved specification
- Access hatches are blocked or sealed in a way that makes service difficult
- The inlet and outlet tees are missing or installed backward
- The flow control fitting is absent or the wrong size
- Cleanout ports are missing
Do not open for food service until both inspections pass and you have a written approval on file. Operating without a valid grease trap inspection approval can result in fines and mandatory closure.
Step 7: Register With the FOG Program
Most municipalities with a pretreatment or FOG control program require food service operators to register after installation. Registration triggers the inspection schedule, typically annual or semi-annual FOG inspections, and adds you to the list of establishments that must submit grease trap service records.
Registration usually involves submitting a form to the local wastewater utility with your business name, address, facility type, and grease trap specifications. Some cities charge an annual FOG program fee, typically $100 to $500.
Keep all installation documentation, the permit, inspection approval, and equipment certification, in your FOG compliance file. You will need this if you are ever audited or if you sell the business.
Grease Trap Installation Costs: What to Budget
| Installation type | Typical cost range |
|---|---|
| Under-sink hydromechanical interceptor (20–50 GPM) | $800–$2,500 |
| Floor-mounted vault interceptor (50–100 GPM) | $2,500–$6,000 |
| Outdoor concrete gravity interceptor (500–1,000 gal) | $8,000–$18,000 |
| Outdoor fiberglass gravity interceptor (1,000–2,000 gal) | $10,000–$25,000 |
| Permit fees | $50–$500 |
| FOG program registration | $0–$500 (annual) |
These ranges are national averages. Urban markets with high labor costs, New York, San Francisco, Chicago, typically run 30 to 50% above these figures.
See our full grease trap installation cost guide for a detailed breakdown by city and unit type.
Common Mistakes to Avoid
Skipping the pre-permit consultation. Calling the local FOG office before you design the installation costs nothing and can prevent expensive rework.
Buying a unit before sizing it. Some operators purchase a unit they found online, then discover it does not meet local certification requirements or is the wrong size.
Letting the unit sit idle before inspection. Water must be running through the trap for the inspection to be meaningful. Do not fill the kitchen with equipment and delay the plumbing, inspectors want to test flow.
Forgetting to notify the FOG program after installation. The permit and plumbing inspection are issued by the building department. FOG program registration is a separate process with a different office. Missing this step means you could receive a notice of violation when the FOG inspector shows up and finds no record of your facility.
Frequently Asked Questions
Do I need a permit to install a grease trap?
Yes, in virtually every U.S. jurisdiction. Commercial grease trap installation requires a plumbing permit from the local building or public works department. Many cities also require pre-approval from the wastewater utility. Operating without a permit can result in fines and mandatory removal and reinstallation.
Can I install a grease trap myself?
No. Grease trap installation on a commercial food service establishment must be performed by a licensed plumber. In many states, the plumber must also hold a specialty certification for grease trap or pretreatment work. Unpermitted work discovered during a FOG inspection can trigger enforcement action.
How long does grease trap installation take?
An indoor hydromechanical interceptor under a sink typically takes 2 to 4 hours of labor. An outdoor gravity interceptor requiring excavation typically takes 1 to 3 days from excavation to backfill, not counting permit processing time.
What size grease trap do I need?
Sizing depends on the number and type of kitchen fixtures, your cooking volume, and local code requirements. A licensed plumber familiar with your local FOG program will run the calculations. Undersizing causes compliance failures; do not guess.
How much does grease trap installation cost?
A small indoor unit runs $800 to $2,500 including labor and materials. A large outdoor concrete or fiberglass interceptor with excavation typically costs $10,000 to $25,000 or more in high-cost markets.
When does a new restaurant need to install a grease trap?
Before the health department issues a food service permit and before you receive a Certificate of Occupancy. Most jurisdictions require the grease trap to be installed, inspected, and registered with the FOG program before the facility opens to the public.
What happens if I fail the grease trap inspection?
The inspector will issue a correction notice listing what needs to be fixed. You reschedule after making the corrections. In most jurisdictions, you cannot legally operate a food service establishment without a passing grease trap inspection.
Conclusion
Installing a grease trap the right way requires sizing, permitting, licensed labor, and a formal inspection, and that process starts before you swing the first wrench. Get the FOG office on the phone early, hire a contractor with local experience, and keep your documentation. If you need to find a licensed grease trap installation contractor in your city, GreaseTrapLocator lists pre-screened professionals across the U.S. and Canada, start your search now.
Author: Grease Trap Locator Editorial Team
The Grease Trap Locator editorial team covers FOG compliance, grease trap maintenance, and commercial kitchen regulations across the US and Canada. Our guides are written for restaurant owners, facility managers, and food service operators who need practical, accurate information without the fluff.
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